1. Field of the Invention
This invention relates to a fluorescent display device, and more particularly to a front emission-type fluorescent display device having an anode formed on one surface of a transparent substrate to allow the emission of a phosphor layer deposited on the anode to be observed through the other surface of the transparent substrate.
2. Description of the Prior Art
A front emission-type fluorescent display device is generally classified into two groups, one having an anode conductor formed of a transparent conductive film such as ITO(indium-tin-oxide) film, tin oxide film or the like and the other having an anode conductor formed of a metallic film.
The present invention is directed to a fluorescent display device of the latter type or the type that an anode conductor is formed by partially removing a metallic film deposited on a substrate by etching or the like and then being provided with transparency. A typical conventional fluorescent display device of such front emission-type is constructed in a manner to provide an anode on a transparent substrate which is formed of a metallic wire into a mesh-like shape corresponding to shape of a display segment to have light-permeable gaps, and deposit a phosphor layer on the anode, to thereby observe emission of the phosphor layer through the transparent substrate.
The conventional display device of this type is capable of significantly reducing voltage drop through a wiring, as compared with that having an anode formed of a transparent conductive film, because the wiring is formed by etching the metallic film.
However, in the conventional fluorescent display device of such type, an insulating material forming a transparent substrate or an insulating layer is exposed at the portion of the substrate which does not have a wiring conductor or a mesh-like anode formed thereon to cause electrons emitted from a cathode to be easily charged on the insulating material. When the charging of electrons occurs on the periphery of the mesh-like anode, electrons subsequently emitted from the cathode are deflected due to a negative electric field generated by the charged electrons to be obstructed from reaching the periphery of the mesh-like anode. This results in a display defect being caused on the periphery of the anode.
In order to obtain distinct and sharp luminous display, a phosphor layer should be deposited on a predetermined area of an anode conductor without any sagging. However, the prevention of such sagging in the conventional display device requires a troublesome indexing operation in a printing process and much time to adjust the viscosity of a phosphor layer in a process of depositing the phosphor layer.
A further disadvantage encounted with the conventional display device of such type is that the use of a printing procedure in the deposition of a phosphor layer on a mesh-like anode causes a phosphor paste to flow out from a predetermined area of the mesh-like anode to the peripheral area thereof due to sagging, so that a display pattern formed fails to have a sharp edge.
The present invention has been made in view of the foregoing disadvantages of the prior art.
Accordingly, it is an object of the present invention to provide a fluorescent display device which is capable of effectively preventing a display defect, allowing a display pattern to have a sharp edge and preventing components received in an envelope of the device from being observed through a substrate to provide excellent visibility.
In accordance with the present invention, there is provided a fluorescent display device comprising a transparent insulating substrate; transparent anode conductors arranged on one surface of the substrate according to a desired display pattern; a phosphor layer deposited on each of the anode conductors which is adapted to emit light when electrons emitted from a filamentary cathode impinge thereon, the light emission of the phosphor layer being observed from the other surface side of the transparent insulating substrate through the transparent anode conductor; a metallic film deposited on the one surface of the substrate; frames each having an inner periphery of a contour corresponding to a display segment corresponding thereto; and display segment openings each having the anode conductor contained therein, the anode conductor having micro-gaps formed therein by partially removing the portion of the metallic film surrounded by the frame; the phosphor layer being deposited to cover at least the display segment opening.